<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        /*此题不涉及继承的权重为0，由权重叠加和优先级来解决
          .c1 .c2 div 权重叠加为 10+10+1=21
          div #box3 权重叠加为  1+100=101
          #box1 div 权重叠加为 100+1=101
          权重相同的，由层叠性可知，颜色为yellow
        */
        .c1 .c2 div{
            color:red;
        }

        div #box3{
            color:blue;
        }

        #box1 div{
            color:yellow;
        }
    </style>
</head>
<body>
   <div id="box1" class="c1">
       <div id="box2" class="c2">
           <div id="box3" class="c3">
               请问这行字体的颜色
           </div>
       </div>
   </div>
</body>
</html>